NoClassDefFound after migrating to Elasticsearch 9.0.2

[FelixHerz]

Java API client version

9.0.2

Java version

21

Elasticsearch Version

9.0.2

Problem description

I am currently migrating our service from Elasticsearch 8.18.2 to 9.0.2.

Unfortunately I get a

Caused by: java.lang.NoClassDefFoundError: org/apache/hc/client5/http/ConnectTimeoutException
	at co.elastic.clients.transport.rest5_client.Rest5ClientTransport.buildRest5Client(Rest5ClientTransport.java:65)
	at co.elastic.clients.transport.rest5_client.Rest5ClientTransport.<init>(Rest5ClientTransport.java:42)
	at co.elastic.clients.transport.ElasticsearchTransportConfig$Default.buildTransport(ElasticsearchTransportConfig.java:110)
	at co.elastic.clients.elasticsearch.ElasticsearchClient.of(ElasticsearchClient.java:188)

When starting the Service.

---

To give you a little context, elastichsearch is wrapped in our own search library:

The pom regarding elasticsearch looks as following:

 <dependencies>
        <!-- Elasticsearch Java API Client -->
        <dependency>
            <groupId>co.elastic.clients</groupId>
            <artifactId>elasticsearch-java</artifactId>
        </dependency>

        <!-- Quite a few more dependencies -->

  </dependencies>

Mvn Dependency Tree gives us:

%  mvn dependency:tree -Dincludes=org.apache.httpcomponents
...
[INFO] --- dependency:3.8.1:tree (default-cli) @ skw-pcs-search-elasticsearch ---
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS

However, when I analyse the dependencies in Intellij it says:

There is a spring boot test in there, which tests against a elasticsearch testcontainer. That test is successfull. All good so far.

---

The library is then used in the service. This is where it all breaks. The maven build is successful but when starting up the service, I get the NoClassDefFound error from above.

Again, mvn dependency:tree doesn't show anything for -Dincludes=org.apache.httpcomponents.

However, I explicitly added it in the pom;

        <dependency>
            <groupId>org.apache.httpcomponents.core5</groupId>
            <artifactId>httpcore5</artifactId>
            <version>5.3.4</version>
        </dependency>
        <dependency>
            <groupId>org.apache.httpcomponents.client5</groupId>
            <artifactId>httpclient5</artifactId>
            <version>5.5</version>
        </dependency>

---

Elasticsearch client is created with:

  @Bean
  public ElasticsearchClient elasticsearchClient(PcsSearchIndexSettings settings) {
    return ElasticsearchClient.of(builder -> builder
                    .host("%s://%s:%d".formatted(
                            settings.getProtocol(),
                            settings.getHost(),
                            settings.getPort()))
    );
  }

[l-trotta]

Hello! This could be a dependency clash caused by other libraries, the java client has an explicit dependency to org.apache.httpcomponents.client5, so it should be found at runtime. Are you getting other exceptions previous to this one, or is there more to the stacktrace? If you're willing to send the compete pom I can see if I can reproduce this and if there's anything we can do on our side to prevent this.

[FelixHerz]

Hi @l-trotta ,

thanks for having a look into it.
Actually I got a bit further by now.
The project is a distributed, multi-module enterprice service, so I can't really paste the pom.

What I did though was

1.) removing elasticsearch-rest-client

<dependency>
    <groupId>org.elasticsearch.client</groupId>
    <artifactId>elasticsearch-rest-client</artifactId>
</dependency>

2.) Moved from httpclient5 v5.5 to v5.4.4

In 2 of 3 services, that actually resolved the issue. In the 3rd it didn't.

Maybe the dependency tree gives any clues ?

dependency-tree.txt

[l-trotta]

I can see that there are conflicts between version 5.4.4 and 5.4.3 of org.apache.httpcomponents.client5:httpclient5, where 5.4.4 is omitted because of 5.4.3, I would try unifying all of the transitive dependency to 5.4.4 by either forcing it or excluding it from the parent dependencies. Not really sure why it does not find ConnectTimeoutException... it should be stable from 5.0. But ideally once you have only one version in the dependency tree it should work properly.